The invention concerns a device for correcting the position of elements of a machine tool and a compensation element used therefor. In machine tools, in particular with an open frame structure (C-shaped), changes in the inclination between the tool side and the workpiece side arise due to different temperature distributions in the components. In particular for multi-spindle machines with which several identical workpieces are intended to be machined simultaneously, this change in inclination results in different dimensions of the individual workpieces, for example, different thicknesses, depending on the machining spindles and the workpieces. The dimensional differences between the individual workpieces can overshoot the predefined tolerances and lead to defective products.
It is a known practice to limit these changes in inclination by cooling systems and to discharge the heat arising at the main heat sources. However, with any expenditure which can be justified the heat arising can never be completely dissipated by a cooling system.
The basic idea of detecting dislocations in machine tools, said dislocations, for example, being caused by the effects of temperature, and compensating them in a well-regulated manner via pressurized deformation elements, is already known from the German patent publication DE 1 946 857 A, in which a process and a device for monitoring and correcting mechanical shifts, in particular in machine tools, is described. For this, one or more deformation elements are disposed at one or more points in the machine. The deformations of the machine tool are determined by analogy starting from a separate detector-deformation element which can be disposed outside of the machine. Between the deformation element and the detector element means for monitoring and regulation are provided. By extending or contracting the deformation elements dislocations are corrected. This solution is relatively complicated and a decisive disadvantage consists in the fact that the deformation elements are formed in a structurally very unstable manner so that, although highly precise manufacturing requires it, the stability of the machine tool is not ensured.
In the German patent publication DE 10 2004 007 042 A1 there is described a device for correcting the position of components in machine tools with headstocks and traversable longitudinal carriages for compensating dislocations which are caused by changes in temperature or static forces. For this the spindle housing is split below the spindle mounting in the central area of the housing and this separation point is once again closed by an adjustment device (actuator), where the actuator can be actuated by a drive. The separation is preferably done at the cross-sectional transition located at the left on the front side of the housing. At the separated partition the required spreading force is transferred by a mechanically programmable actuator. In order to be able to selectively set the desired inclination correction at the spindle flange the machine-specific temperature behavior is evaluated via the control and thereafter via the programmable actuator the spreading force necessary for the change is applied. In so doing, the actuator is deformed via a threaded spindle with two different pitches to generate the spreading load and thereby the working spindle is inclined. For this the threaded spindle is moved by a drive unit by the required adjustment travel. Serving as drive unit is a positioning drive which comprises a DC motor with an absolute value transmitter, an integrated control and power electronics, and a differential rack gear set in front. This unit is fastened on a motor bearing. Depending on the temperature which is recorded by a sensor the positioning drive, which via the actuator generates the spreading force necessary for changing the inclination of the spindle housing, is controlled via the machine control. Thus the inclination of the spindle is corrected by the required amount. Therein the actuator is not implemented in a very compact manner so that this is disadvantageous for stability. Furthermore, the inclination adjustment of the working spindle is done exclusively as a function of the measured temperature. Any undesirable changes in position which, in given cases, can occur due to other influencing factors, are not detected.
The main problem in the use of the aforesaid solutions is furthermore the loss of rigidity in the degree of freedom in which the compensation acts, as well as in other spatial degrees of freedom. Thus with this device for position correction a type of “floating positioning” with reduced rigidity is realized in every case, whereby the precision of production is negatively affected despite the position or inclination compensation having been carried out.
A device for correcting the dislocation of a translationally movable part, e.g. a carriage, a slide feed, a ram, or the like on a machine tool for cutting metal is known from the German patent publication DE 34 23 495 C2. The machine tool comprises a perpendicular column, a headstock which can be traversed along the column, and the movable part slidingly borne by the headstock and on which a workpiece or an additional device can be fastened.
In this solution the following components are provided:
pressurized with a pressurizing agent, a device for applying a corrective force for correcting the effect caused by the dislocation of the movable part,
a position detection device for detecting the position of the movable part,
a device for generating a dislocation correction value as a function of the detected position of the movable part, and
actuated depending on the dislocation correction value, a valve for setting the pressure of the pressurizing agent,
where the device for applying a corrective force comprises a compensation device for correcting an inclination of the movable part and the position detection device generates a position signal, and where the device for generating a dislocation correction value is a calculation device which generates a dislocation correction signal. The valve can be actuated electromagnetically by the dislocation correction signal and the device for applying a corrective force comprises a compensation device for correcting any bending of the movable part, a compensation device for correcting a headstock inclination caused by a shift of the position of the center of mass of the headstock and a compensation device for correcting an elastic deformation of the front lower section of the headstock. A calculation device supplied with the position signal performs an automatic evaluation of the load changes occurring on the movable part and provides for an optimal functional relationship between the movable machine tool part's shifted position represented by the position signal and the dislocation correction values for the individual compensation devices. In this way even for machine tools with large dimensions and heavy weight using relatively simple control means the effect caused by the dislocation of the movable machine tool part is intended to be corrected. This solution is configured in a relatively complicated manner and it is very complicated to compensate the bending of the movable part, here the axially traversable spindle.
It is the object of the invention to provide a simple device for correcting the position of elements of a machine tool, in particular a milling machine, and which ensures a high rigidity of the machine.
In the device according to the invention and for correcting the position of at least one element of a machine tool, in particular a milling machine, between a machine element and the element to be corrected with respect to its position, at least one compensation element is disposed, which can be traversed by an adjustment travel, and by actuating the compensation element by an adjustment travel the element can be pivoted about a pivot axis and where the machine element and the element to be corrected in its position are coupled to one another by a joint ensuring the pivoting movement about the pivot axis.
Due to the fact that the element which can be adjusted in its position is actuated via the compensation element and can be pivoted and stabilized by the joint, the rigidity of the machine is impacted only insignificantly.
If the machine tool in the form of a milling machine is formed with an, in particular open, C-shaped frame structure with a first structural part to which is assigned at least one working spindle with a spindle axis and a tool which can be driven about the spindle axis and with at least one second structural part to which is assigned at least one clamping device for at least one workpiece, then the inclination between the first and second structural part can be changed due to the fact that the first and/or second structural part forms or form or comprises or comprise the element which can be changed in its position and can be changed in their inclination relative to one another by one or more compensation elements through the induced pivoting movement about the pivot axis.
In so doing, the tool or tools disposed on the first structural part are aligned to one another in particular in a tool clamping plane inclined by 90° relative to the spindle axis and the workpiece or workpieces are aligned in a workpiece clamping plane, where the tool clamping plane and the workpiece clamping plane are aligned essentially parallel to one another. If between the tool clamping plane and workpiece clamping plane there is an inclination overshooting a predefined tolerance this inclination is compensated by correcting the inclination of the first structural part or an area of the first structural part and/or correcting the inclination of the second structural part or an area of the second structural part.
Preferably the element which can be adjusted with respect to its inclination is formed as a first part of the second structural part on which the clamping device for the workpiece is located, where a second part of the second structural part forms the machine element and the first part and the second part of the second structural part are pivotably connected to one another by the joint and between the first part and the second part of the second structural part several compensation elements are disposed. Due to the fact that there is pivoting of the machine tool's structural part on which the tool clamp is disposed, an essentially simpler inclination compensation is possible than for an inclination adjustment of the machine element on which the headstock with the entire drive technology for the tools is located.
In connection with this the joint is in an advantageous manner disposed on the second structural part's side facing the first structural part and is formed as a play-free flexure bearing, in particular consisting of sheet metal, and is fastened on the first part and the second part of the second structural part.
On the second structural part's side opposite the joint several compensation elements are disposed next to one another between its first part and second part, where preferably each two compensation elements are used as a pair and at a distance from one another two compensation elements or two pairs of compensation elements are disposed between the first part and the second part of the second structural part and where the separating line between the first part and the second part of the second structural part is aligned essentially horizontally.
A simple and practical possibility for determining the inclination or change in inclination between the two planes consists in the fact that it can be determined with a machine-internal measurement system and that from the value or values determined the magnitude of the adjustment travel of the compensation elements is calculated.
For simultaneously machining in particular structurally identical workpieces which are clamped on the second structural part the first structural part has a corresponding number of working spindles. For machining, for example, two workpieces disposed one over another with two tools disposed one over another, the inclination compensation is of particular importance since for too large an inclination between the workpiece clamping plane and the tool clamping plane the results of machining the workpieces can deviate from one another so undesirably that defective products occur.
The compensation element which is according to the invention and which is used for correcting the position of at least one element of a machine tool, in particular a milling machine, can be traversed by an adjustment travel and is disposed between a machine element and the element to be corrected with respect to its position and comprises an essentially tubular elongated body with a thin wall and a longitudinal axis aligned to the direction of the adjustment travel, where a supporting body is disposed within the elongated body and a pressure chamber is formed between the supporting body and the elongated body in such a manner that with a pressure force changing and acting in the pressure chamber of the elongated body the thin wall of the elongated body is changed in its length in the adjustment direction by the adjustment travel and thereby the element is adjusted in its position/inclination. Due to the disposition of a supporting body in the elongated body along with axial adjustability, high stability and rigidity of the compensation element is ensured and thus with its use the rigidity of the machine tool is impacted only insignificantly which for a good machining result in particular when high precision is required is an essential prerequisite.
Preferably the elongated body and the supporting body are connected to one another at a first end of the compensation element and at the other second end of the compensation element the pressure chamber is formed between the outer contour of the supporting body and the inner contour of the elongated body.
For this the supporting body and the elongated body each have at the second end of the compensation element a base, where between the bases the pressure chamber is formed so that with a force changing and acting in the pressure chamber against both bases the total height of the compensation element changes.
Along with this the force acting in the pressure chamber and generating the adjusting movement can optionally be induced by the pressurization of the pressure chamber, which is sealed by a seal and comprises a pressurizing agent conduit, by pressurizing medium or by a piezoelectric element which is disposed in the pressure chamber and which can be adjusted in its height by application of a voltage or by an element which is disposed in the pressure chamber and can be adjusted in its height mechanically.
With the solution according to the invention an extremely simple and practical solution for adjusting the inclination of a machine element is provided with which the stability of the machine is not impacted or is impacted only insignificantly.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.